“It’s a tough disease to diagnose,” says Marie Budev, DO, a pulmonologist and the medical director of the lung transplant program at the Cleveland Clinic in Ohio. “Age makes a big difference, as well as a person’s immune status … and, of course, the symptoms themselves,” which often mimic those of a cold or flu.

The first thing a doctor will do is use a stethoscope to listen for crackling or bubbling sounds in the lungs. “Decreased breath sounds is an indication of a lot of inflammation,” says Michelle Barron, MD, an associate professor in the division of infectious diseases at University of Colorado in Denver. A chest X-ray can help determine the extent of the infection, while blood tests and an analysis of the patient’s sputum can pinpoint what’s causing the pneumonia.

How Common Is Pneumonia?

According to the Centers for Disease Control and Prevention (CDC), about one million Americans are hospitalized each year due to pneumonia, making it the second most frequent cause of hospitalizations in the country. (1)

Although pneumonia generally responds well to treatment, 15 percent of these cases are fatal, the CDC reports.

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In the United States, pneumonia and the flu jointly rank as the eighth-leading causes of death.

“The lung is a large organ, and it’s a vital organ,” says Gerard Criner, MD, chair and professor of thoracic medicine and surgery at Temple University School of Medicine in Philadelphia. “If it gets infected and it compromises the primary function to support ventilation, that’s a big contributor to morbidity and mortality.”

What Are the Risk Factors for Pneumonia?

Young children and people older than 65 are the most vulnerable to pneumonia. (2)

You're also at higher risk for pneumonia if you have any of the following conditions:

People who smoke are also at much higher risk for pneumonia, regardless of age, and the condition is more likely to afflict men and African-Americans.

The majority of the germs that cause pneumonia are spread from person to person through droplets, from coughing or sneezing.

People who are frequently in close contact with others, such as college students and military personnel, are also more susceptible to the disease.

There are measures you can take to reduce your risk of developing and transmitting pneumonia:

Practice good hygiene. Simple precautions, such as washing your hands frequently, covering your nose and mouth with a tissue when you cough or sneeze, and disposing of used tissues cut down exposure and spread of germs.

Don’t smoke. “Smokers are at a much greater risk of getting pneumonia because the protective mechanisms that your lungs set up to escalate debris out of your lungs are just paralyzed by tobacco,” says Jason Turowski, MD, a pulmonologist and associate director of the adult cystic fibrosis program at the Cleveland Clinic in Ohio.

Get vaccinated.Pneumococcal vaccines protect against one of the most common causes of bacterial pneumonia, and the flu shot can help avoid influenza-related pneumonia. Getting vaccinations “is the most important thing you can do,” Dr. Turowski says.

What Types of Pneumonia Are There?

The severity of the infection depends on many factors, including your age and overall health.

“A lot of treatment aspects, as well as outcome, depend on the person, as well as the type of pneumonia they have,” says Dr. Barron. “Sometimes you’ll be fine just resting, but if you have things like trouble breathing, you should get to a doctor right away.”

Knowing the cause of a lung infection is important for determining which type of pneumonia you have, how you got it, and how to treat it.

Here's what you need to know about the different types of pneumonia:

Community-Acquired Pneumonia

Also known as CAP, this is the most common form of pneumonia because you can catch it in public places, such as at school or work. It can be caused by bacteria, viruses, or fungi. (4)

You can also develop CAP after you get a common viral infection, such as a cold or the flu.

The illness ranges from mild to serious and, if left untreated, can lead to respiratory failure or death.

Bacterial CAP is usually more serious than other types and is more common among adults. Atypical pneumonia, often called walking pneumonia, is a milder form.

Viral and bacterial pneumonia share some common signs, but doctors can often distinguish between them by a patient’s symptoms.

Various types of bacteria are responsible for the illness. In most cases, the bacteria will enter the lung during inhalation, but it can also go through the bloodstream if other parts of the body are infected.

Streptococcus pneumoniae, also known as pneumococcal pneumonia, can be treated with antibiotics. But according to the CDC, many types of bacteria, including some S. pneumoniae (pneumococcus), are resistant to those antibiotics, which can lead to treatment failures. Pneumococcal pneumonia causes up to 175,000 hospital admissions a year in the United States. (5)

You can also have a pneumococcal infection without having pneumonia. For example, pneumococcal infections also cause more than three million ear infections in children every year.

Depending on how sick you are and whether or not you have any other health conditions, your doctor may treat you for bacterial pneumonia with antibiotics either at home or in the hospital.

Viral CAP, particularly the respiratory syncytial virus (RSV), is the most common cause of pneumonia in children younger than two years old. (6)

Although viral pneumonia is generally less severe than bacterial pneumonia, viral infections caused by certain flu viruses, such as severe acute respiratory syndrome (SARS), can be very serious.

Antibiotics are ineffective against viral pneumonia. Your doctor will most likely treat the symptoms — fever, cough, and dehydration.

You or your child may need to be hospitalized if your viral pneumonia symptoms become severe.

Fungal CAP is most common in people with an underlying health problem or a weakened immune system, including those with HIV or AIDS and people undergoing treatment for cancer. It's treated with antibiotics or antifungal medication. (7)

Healthcare-Associated Pneumonia

This refers to an infection that develops in someone being cared for in a healthcare facility, such as a hospital or nursing home. If you've been hospitalized or admitted into a long-term nursing or rehab facility, you may be at risk for more deadly forms of pneumonia. (8)

Symptoms of this type of pneumonia are more serious and may include shortness of breath, high fever, and chest pain.

Hospital-Acquired Pneumonia

As the name suggests, this develops during a hospital stay for a different health problem. People who are on machines to help them breathe are particularly prone to developing hospital-acquired pneumonia.

Hospital-acquired pneumonia usually needs to be treated in the hospital with intravenous antibiotics.

Aspiration Pneumonia

This can develop after a person inhales food, liquid, gases, or dust.

A strong gag reflex or cough will usually prevent aspiration pneumonia, but you may be at risk if you have a hard time swallowing or have a decreased level of alertness.

A form of aspiration pneumonia, chemical- or toxin-related pneumonia is caused by the inhalation of chemical fumes, as through an exposure to a mix of ammonia and bleach, or in the breathing in of kerosene or some other noxious chemical.

This type of pneumonia can also occur in older people with poor swallowing mechanisms, such as stroke victims, who actually can inhale the acidic contents of their stomachs, causing aspiration pneumonia.

This causes inflammation without bacterial infection. These pneumonias can sometimes be difficult to treat, especially because the patients are sicker to begin with.

Once your lungs have been irritated by breathing in food or stomach contents, a bacterial infection can develop.

Some conditions that may put you at risk for aspiration pneumonia include:

Treatment may include breathing assistance and intravenous antibiotics given in the hospital.

You can prevent complications by not eating or drinking before surgery, working with a therapist to learn how to swallow without aspirating, and avoiding heavy use of alcohol.

Opportunistic Infection

Finally, pneumonia that develops in people with a weakened immune system is often referred to as an opportunistic infection.

You're more at risk for this type of pneumonia if you have a chronic lung disease, have HIV or AIDS, or have had an organ transplant.

What Are the Symptoms and Causes of Pneumonia?

There are more than 30 different causes of pneumonia, including bacteria, viruses, airborne irritants, and fungi. (8) When these germs enter the lungs, they can overwhelm the immune system and invade nearby lung tissues, which are very sensitive. Once infected, the air sacs in the lungs become inflamed, causing coughing, fever, chills, and breathing problems.

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If you have persistent or worsening flu-like symptoms, talk to your doctor. And if you have difficulty breathing, go to the emergency room right away. Pneumonia can become severe if left untreated.

People with severe pneumonia experience higher fevers along with gastrointestinal symptoms, such as vomiting and diarrhea. Sweating, rapid heart rate, and a bluish tint to lips and nails are also signs of severe pneumonia.

How Does Pneumonia Differ in Children?

Pneumonia symptoms in children may show up differently and be harder to recognize than symptoms in adults. Symptoms vary with age, and children may not have a persistent cough or high fever — but headache, sore throat, fatigue, and loss of appetite could indicate they’ve got more than a bad cold and that they need medical attention.

Children are at greater risk of contracting the disease because their immune systems aren't fully developed. And pneumonia can progress very quickly among children, particularly infants and those with underlying medical conditions. (9)

How Do You Treat and Prevent Pneumonia?

Effective treatment of pneumonia depends on what caused the infection, and can range from outpatient care to surgery. (10) Some people may only need bed rest, while others may require a hospital stay. Your doctor will outline a plan that's specific to you, considering the type of pneumonia you have, the severity of the condition, your age, and your overall health. From there, you'll know whether you can be treated at home or must go to the hospital, and whether or not you need antibiotics. (11)

How Do You Know if It’s Pneumonia?

Pneumonia shares many symptoms with the common cold and influenza, or flu, but there are key differences that are critical to diagnosing and treating each. The basic differences come down to whether you can prevent and treat the disease, and how serious the consequences can be, according to Aaron M. Milstone, MD, assistant professor of pediatric infectious diseases at Johns Hopkins Children's Center in Baltimore.

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With the common cold, there's no vaccine to prevent it, but it’s not typically serious and symptoms are mild. The flu and pneumonia, on the other hand, can have serious consequences and more severe symptoms. Both are associated with a much higher rate of hospitalization, and even death, than the common cold.

Common Pneumonia Terms You Should Know

It’s important to understand the facts about pneumonia, as it can be very serious, if not life-threatening. Because pneumonia has several different causes, types, and treatments, the terminology may be confusing.